1. Field of the Invention
The invention is in the field of automatic welding machines and more particularly in the field of automatic welding machines which include a welding torch attached to a torch transporting carriage.
2. Description of the Prior Art
There are automatic welding machines for welding flat plates and automatic welding machines for welding pipes. In either of such automatic welding machines a welding torch is attached to a torch transporting carriage. The carriage is mounted to a rail by means of at least one pair of opposed wheels which are clamped to opposite sides of the rail. A drive source, such as an electric motor, is connected to an axle of one of the whels to drive the carriage along the rail through the drive wheel. A pinion may be connected to the drive axle receiving power from the drive source. The pinion cooperates with a rack provided on the rail to facilitate movement of the carriage.
A conventional automatic welding machine and specifically an automatic welding machine for welding flat plates is illustrated in FIGS. 1 through 3. FIG. 1 illustrates a front view of such a welding machine, while FIG. 2 illustrates a plan view of the welding machine of FIG. 1. FIG. 3 is an enlarged sectional view of the drive mechanism section for driving the carriage with power from a drive source.
More specifically, the automatic welding machine of FIGS. 1-3 includes a rail 1 with a rack 2 extending along the longitudinal center line of the rail. A torch transporting carriage 3 is adapted to run on the rail 1 by means of a first pair 4a and a second pair 4b of guide wheels. Each pair of guide wheels is amounted on a respective axle 5a and 5b. Thus, as can be seen in FIG. 2, the wheels run along th top sides of the rail 1 with their respective axles straddling the rack 2. A pinion 6 is mounted on one of the axles 5a in such a manner as to engage the rack 2. A welding torch 7 secured to the carriage 3 by a torch mounting board 8 is transported to selected welding sites by the carriage. The carriage 3 further includes a clamping frame portion 9 with wheels 10a and 10b which roll on the lower surface of the rail 1. The clamping frame 9 is connected to the carriage 3 by means of threaded rods 11 which pass through holes 12 in flange portions at the front and rear of the top portion of the carriage 3 and attach to the front and rear of the clamping frame 9. Threaded clamping pressure actuating members 13 are screwed onto the threaded bars 11 after they are inserted through the holes 12. The carriage is clamped to the rail with a suitable force by adjusting the screwed-down position of the members 13.
As illustrated in FIG. 2, power from the drive axle 5a can be transmitted to the driven axle 5b through a sprocket and chain arrangement consisting of the sprocket 20 on axle 5a, sprocket 22 on axle 5b and the chain 21.
The drive axle 5a receives power from a suitable drive source such as an electric motor 14 through gears 16 and 17 contained in a gear box 15. When the motor is started, gears 15, 16 rotate causing the axle 5a and its pinion 6 to rotate. As the pinion 6 engages the rack 2 of the rail 1 the torch transporting carriage 3 will run along the rail. In this way, the welding torch 7 is moved into various positions facing parts to be welded.
A problem with such a conventional automatic welding machine is that there is an unavoidable backlash in the drive system so that after the carriage has been moved a specified distance in a first or forward direction under power provided by the drive source and thereafter, the drive source power is removed, the carriage has a tendency to move backwards in the direction opposite to the first direction. This results in imprecisely locating the carriage for welding operations. In addition, should the rail not be perfectly level, the carriage may roll out of position when the drive source power is removed, again mislocating the welding torch for the required welding operation.